Type 347H is a high carbon austenitic chromium stainless steel. Found in applications that demand high temperature resistance, other major design features include:
Similar resistance and corrosion protection as Alloy 304
Used for heavy welded equipment when annealing is not possible
Good oxidation resistance, on par with most other austenitic stainless steels
Higher carbon allows for better high temperature creep properties
Chemical Composition
The following table shows the chemical composition of grade 347H stainless steel.
| Element | Content (%) |
|---|---|
| Iron, Fe | 62.83 - 73.64 |
| Chromium, Cr | 17 - 20 |
| Nickel, Ni | 9 - 13 |
| Manganese, Mn | 2 |
| Silicon, Si | 1 |
| Niobium, Nb (Columbium, Cb) | 0.320 - 1 |
| Carbon, C | 0.04 - 0.10 |
| Phosphorous, P | 0.040 |
| Sulfur, S | 0.030 |
Fabrication and Heat Treatment
Machinability
Machining grade 347H stainless steel is slightly tougher than that of grade 304 steel. However, the hardenability of this steel can be minimized by the use of constant positive feeds and slow speeds.
Welding
Grade 347H stainless steel can be welded using most of the resistance and fusion methods. Oxyacetylene welding is not preferred for this steel.
Hot Working
Forging, upsetting and other hot work processes can be performed at 1149 to 1232°C (2100 to 2250°F). The grade 347H steel has to be water quenched and annealed to obtain maximum hardness.
Cold Working
Grade 347H stainless steel can be readily stamped, blanked, spun and drawn as it is quite tough and ductile.
Annealing
Grade 347H stainless steel can be annealed at temperature ranging from 1010 to 1193°C (1850 to 2000°F) and then quenched with water.
Hardening
Grade 347H stainless steel is unresponsive to heat treatment. The hardness and strength of the steel can be increased through cold working.
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